Good afternoon!
Tomorrow: Background Quiz (PICK UP YOUR
QUESTIONS ON YOUR WAY OUT TODAY!)
Directions
O As you go through the slides, fill in the definitions on the
lines in your packet.
O You have a test over logical fallacies Wednesday, April
24th. These notes will be the basis of what you will need
to study in order to be successful on the test.
O There is no need to talk, be disruptive, etc. while taking
notes unless you have a question. The faster you
complete the notes, the sooner we can all move on with
our lives!
Fallacies
A fallacy is an error
in reasoning.
Some fallacies are so
common that they have
names of their own.
SECTION I
Appeals to Motives in the
Place of Support
The fallacies in this section have in common the practice of appealing
to emotions or other psychological factors. In this way, they do not
provide reasons for belief.
Ad Misericordiam
(Appeal to Pity)
The reader is told to agree to the proposition because of
the pitiful state of the author.
O Examples:
O How can you say that is out? It was so close, and
besides, I'm down ten games to two.
O We hope you will accept our recommendations.
We spent the last three months working extra time
on it.
B UY THIS SAD, NEGLECTED K ITTY.
Ad Populum
(Bandwagon)
O The arguer appeal to the popularity of an
idea or of an attitude as a justification.
O Note that voting and majority rule are not so
much methods to establish a truth, as a
decision procedure that it accepted because
it is fair. Truth is not decided by a vote.
Ad Populum Examples
 If you were beautiful, you could live like this,
so buy Buty-EZ and become beautiful.
(Here, the appeal is to the “beautiful
people".)
 Polls suggest that the Liberals will form a
majority government, so you may as well
vote for them.
 Everyone knows that the Earth is flat, so
why do you persist in your outlandish
claims?
SECTION II
Changing the Subject
The fallacy in this section changes the subject by discussing the
person making the argument instead of discussing reasons to
believe or disbelieve the conclusion. While on some occasions it is
useful to cite authorities, it is almost never appropriate to discuss
the person instead of the argument.
Ad Hominem
 Ad hominem means, literally, “to the man”.
 Ad hominem occurs when, instead of
attacking a person’s position or argument,
the arguer attacks the person on irrelevant
grounds.
 It is the attempt to discredit an idea or
proposition by pointing to some flaw or fault
in the behavior or character of the person
who is the source of the idea or proposition.
Ad Hominem Examples
 You may argue that God doesn't exist, but you are
just following a fad.
 We should discount what Premier Klein says about
taxation because he won't be hurt by the increase.
 We should disregard Share B.C.'s argument because
they are being funded by the logging industry.
 After Sally presents an eloquent and compelling
case for a more equitable taxation system, Sam
asks the audience whether we should believe
anything from a woman who isn't married, was once
arrested, and smells a bit weird.
Ad Verecundiam
(Appeal to Authority)
O Definition: While sometimes it may be appropriate to cite an
authority to support a point, often it is not. In particular, an
appeal to authority is inappropriate if:
O the person is not qualified to have an expert opinion on the
subject,
O experts in the field disagree on this issue.
O the authority was making a joke, drunk, or otherwise not
being serious
O A variation of the fallacious appeal to authority is hearsay. An
argument from hearsay is an argument, which depends on
second or third hand sources.
Ad Verecundiam Examples
O Noted psychologist Dr. Frasier Crane recommends that you buy the EZO
O
O
O
Rest Hot Tub.
"UFOs are not real, because the great Carl Sagan said so."
Economist John Kenneth Galbraith argues that a tight money policy is
the best cure for a recession. (Although Galbraith is an expert, not all
economists agree on this point.)
We are headed for another war. Last week a noted politician remarked
that we begin bombing Korea in five minutes.
My friend heard on the news the other day that Canada will declare war
on Serbia. (This is a case of hearsay; in fact, the reporter said that
Canada would not declare war.)
SECTION III
Inductive Logic
Inductive reasoning consists of inferring from the properties of a
sample to the properties of a population as a whole.
No inductive inference is perfect. That means that any inductive
inference can sometimes fail. Even though the premises are true,
the conclusion might be false. Nonetheless, a good inductive
inference gives us a reason to believe that the conclusion is
probably true.
Hasty Generalization
The size of the sample is too small to support the conclusion.
O
Examples:
O Fred, the Australian, stole my wallet. Thus, all Australians are
thieves. (Of course, we should not judge all Australians based on
one example.)
O I asked six of my friends what they thought of the new spending
restraints and they agreed it is a good idea. The new restraints
are therefore generally popular.
SECTION IV
Fallacy of Ambiguity
This is a case where a word or phrase is used unclearly.
This can occur in two ways.
• The word or phrase may be ambiguous, in which case it
has more than one distinct meaning.
• The word or phrase may be vague, in which case it has no
distinct meaning.
Accent
O Definition: Emphasis is used to suggest a
meaning different from the actual content of
the proposition. Accent is a kind of fallacy of
ambiguity.
O Example:
It would be illegal to give away
FREE BEER!
SECTION V
Other Causal Fallacies…
It is common for arguments to conclude that one thing
causes another. However, the relation between cause
and effect is a complex one. It is easy to make a
mistake. In general, we say that a cause C is the cause
of an effect E if and only if:
Generally, if C occurs, then E will occur, and
• Generally, if C does not occur, then E will not occur
either. We say "generally" because there are always
•
exceptions, hence the fallacy in logic.
Slippery Slope
In order to show that a proposition P is unacceptable,
a sequence of increasingly unacceptable events is
shown to follow from P. A slippery slope is an
illegitimate use of the "if-then" operator.
Slippery Slope Examples
O If we pass laws against fully automatic weapons, then it will
not be long before we pass laws on all weapons, then we
will begin to restrict other rights, and finally we will end up
living in a communist state. Thus, we should not ban fully
automatic weapons.
O You should never gamble. Once you start gambling you find
it hard to stop. Soon you are spending all your money on
gambling, and eventually you will turn to crime to support
your earnings.
Post hoc, ergo propter hoc
O Literally, “after this, therefore because of
this”.
O Committing this fallacy occurs when one
confuses correlation with causation.
Post hoc, ergo propter hoc
Examples
O Immigration to Alberta from Ontario
increased. Soon after, the welfare rolls
increased. Therefore, the increased
immigration caused the increased welfare
rolls.
O I took EZ-No-Cold, and two days later, my
cold disappeared.
False Dilemma
O Giving a limited number of options when
there are in fact more options available.
Examples:
O “Either you're for me or against me”.
O “America: love it or leave it”.
O “Every person is either wholly good or wholly
evil”.
SECTION VI
Missing the Point
These fallacies have a general failure to
prove that the conclusion is true.
Begging the Question
O This fallacy occurs when, instead of giving a
reason that establishes the conclusion, the
conclusion is simply assumed. The premise is
just another way of stating what is supposed to
be proved.
O Also known as
circular reasoning
Begging the Question
Examples
O “Since I'm not lying, it follows that I'm telling
the truth.”
O “We know that God exists, since the Bible
says God exists. What the Bible says must
be true, since God wrote it and God never
lies.” (Here, we must agree that God exists
in order to believe that God wrote the Bible.)
Sweeping Generalization
(Accident)
The fallacy of accident is sometimes also called a
sweeping generalization and this latter name for
it gives an indication of what is going on. It occurs
when a general rule is misapplied to a particular
situation.
O For example: The Bible says, "thou shalt not
kill", but every time you eat you're killing
something.
The End…
Now that that’s over…
You have time to read Animal Farm
and work on your study guide.
Remember: Background quiz
TOMORROW!